In the past an acrylonitrile-butadiene-styrene resin (abbreviated below as ABS resin) was generally used as the resin used for toilet components. This ABS resin had excellent properties, e.g., a high stiffness, high impact resistance, and high gloss, but also had the problem of an inferior chemical resistance, e.g., acid resistance and alkali resistance, and in particular had an inferior acid resistance.
Detergents having an improved cleaning performance have been developed and used in recent years in order to remove the causes of staining in the toilet environment, for example, microorganisms due to the adhesion of urine or fecal matter, stains due to mold growth, the urea, phosphate salts, and crude proteins in urine stain components, discharges from patients during periods of drug intake, excretion of excess vitamins due to excessive consumption of soft drinks, and the organics in urine and fecal matter, and also water stains, blood, toilet cleansers, flush toilet cleansers, and so forth. However, this has produced the problem of discoloration and a deterioration in mechanical properties—as well as cracking in extreme cases—with toilet components made of ABS resin and particularly with the cleaned-daily toilet lid and toilet seat.
On the other hand, the use of polypropylene-based resins, which have an excellent chemical resistance among thermoplastic resins, is also known as an avenue for addressing such problems.
However, general polypropylene-based resins were not completely satisfactory with regard to properties such as the stiffness and gloss as for ABS resins, tactile sensation, marring resistance, and a discoloration resistance that would resist the discoloration caused by urine, fecal matter, and detergents, and improvements in these areas were strongly desired.
Various means have been proposed as attempts to solve these problems with polypropylene-based resins (refer, for example, to Patent Documents 1 to 5).
For example, Patent Document 1 discloses that the incorporation of 0.01 to 1 weight part of a hindered amine stabilizer and 0.01 to 1 weight part of an aromatic phosphorus-type antioxidant in 100 weight parts of a polypropylene resin provides a polypropylene resin composition that is resistant to the discoloration caused by urine, fecal matter, and detergents and that exhibits an excellent tactile sensation, an excellent resistance to thermal ageing, and an excellent resistance to detergents.
Patent Document 2 discloses that the incorporation of 0.01 to 1 weight part of a hydroxylamine-type compound and 0.05 to 1 weight part of a hindered amine photostabilizer in 100 weight parts of a polypropylene-based resin provides a polypropylene resin composition that yields moldings free of urine-induced discoloration and that exhibits little scorching during processing.
Patent Document 3 discloses a stain-resistant polypropylene resin composition that exhibits an excellent resistance to staining and that comprises a polypropylene resin, a polar group-containing silicone oil, and a compatibilizer that improves the compatibility between the polypropylene resin and the polar group-containing silicone oil, wherein the polar group-containing silicone oil is dispersed in the polypropylene resin.
Patent Document 4 discloses a resin composition that is resistant to urine-induced discoloration and that is well suited for materials such as toilet seats and toilet lids and has an excellent resistance to urine-induced discoloration, an excellent heat resistance, and an excellent ageing resistance. This resin composition is a polypropylene-based resin and, per 100 weight parts thereof, 0.2 to 10 weight parts of a white pigment, e.g., titanium oxide, zinc oxide, and so forth, 0.02 to 2 weight parts of a hindered amine compound having a molecular weight of at least 1,500, and not more than 0.02 weight parts of a phenolic antioxidant.
Patent Document 5 discloses a polypropylene-based resin composition for toilet seat components that exhibits a satisfactory inhibition of warpage by toilet seat components, a satisfactory inhibition of the discoloration induced by urine, fecal matter, and detergents, an excellent tactile sensation, excellent warping characteristics, an excellent stiffness, and also an excellent resistance to thermal ageing and an excellent resistance to detergents. This resin composition is obtained by incorporating 0.01 to 1 weight part of a nucleating agent in 100 weight parts of a highly crystalline polypropylene-based resin that has an isotactic pentad fraction of at least 96%, and the resin composition has a prescribed melt flow rate (MFR) and a prescribed memory effect (ME) and has a crystallization temperature of 125 to 136° C.
Heated toilet seats have, however, become predominant, and this also has been accompanied by a requirement for flame retardancy in the polypropylene-based resin compositions that are used for toilet components (toilet seat components). A brominated flame retardant and antimony trioxide as a flame retardant synergist have heretofore been incorporated in combination in order to impart flame retardancy to polypropylene-based resins, and such flame-retardant polypropylene-based resins are widely used as general-purpose flame-retardant resins in diverse molded articles where flame retardancy is required.
However, in addition to molding defects, such as the appearance of silver streaks, caused by decomposition gases from the flame retardant, the problem has arisen of the generation of appearance defects in the surface of molded articles due to scorching. Various means have been proposed as attempts to solve these problems with flame-retardant polypropylene-based resins (refer, for example, to Patent Documents 6 to 9).
For example, Patent Document 6 discloses a flame-retardant polypropylene-based resin molding adapted for toilet seat components, that exhibits an excellent moldability and that is free of the appearance of molding defects such as silver streaks even when fast-fill molding is performed. This is achieved by a resin molding that is molded from a flame retardant-containing polypropylene-based resin composition, wherein this resin composition has a prescribed melt flow rate (MFR), a prescribed memory effect (ME), and a prescribed density.
In addition, Patent Document 7 discloses a polypropylene-based resin composition that is adapted for applications such as toilet seats and toilet lids and that yields molded articles that have an excellent surface appearance wherein the generation of, e.g., silver streaks and scorching, is inhibited. This polypropylene-based resin composition contains (A) a prescribed high-crystallinity propylene-based polymer I and, per 100 weight parts thereof, 1 to 25 weight parts of (B) a propylene-based polymer II that has an MFR of 1 to 20 g/10 minutes, a Q value of at least 7, and a ratio (Mz/Mw) of the Z-average molecular weight (Mz) to the weight-average molecular weight (Mw) of at least 5; 3 to 50 weight parts of (C) an organic flame retardant; 1 to 40 weight parts of (D) an antimony compound; and 0.01 to 0.5 weight parts of (E) a silicone oil.
Patent Document 8 discloses a crystalline polypropylene resin composition that is well suited for applications such as toilet seats and toilet lids and that yields molded articles that have an excellent surface appearance wherein the generation of, e.g., silver streaks and scorching, is inhibited. This composition contains (A) a prescribed crystalline polypropylene and, per 100 weight parts thereof, 1 to 25 weight parts of (B) a propylene-based polymer that has an MFR of 0.01 to 100 g/10 minutes, a Q value of 3.5 to 10.5, a content of the component with a molecular weight (M) of at least 2,000,000 of at least 0.4 weight % but less than 10 weight %, not more than 3.0 weight % component that elutes at a temperature less than or equal to 40° C. in temperature-rising elution fractionation (TREF), an isotactic triad fraction (mm) of at least 95%, and a strain hardening (λmax) in measurement of the extensional viscosity of at least 6.0; 3 to 50 weight parts of (C) an organic flame retardant; and 1 to 40 weight parts of (D) an antimony compound.
Patent Document 9 discloses a crystalline polypropylene resin composition that is well suited for applications such as toilet seats and toilet lids and that yields molded articles that have an excellent surface appearance wherein the generation of, e.g., silver streaks and scorching, is inhibited. This composition contains (A) a prescribed crystalline polypropylene and, per 100 weight parts thereof, 1 to 25 weight parts of (B) a propylene-based polymer that has prescribed properties and is constituted of a prescribed component (a) that is insoluble in p-xylene at 25° C. and a prescribed component (β) that is soluble in p-xylene at 25° C.; 3 to 50 weight parts of (C) an organic flame retardant; and 1 to 40 weight parts of (D) an antimony compound.
As previously noted, it is difficult with a general polypropylene-based resin to generate the gloss and marring resistance of ABS resin, and a tactic for dealing with this is to generate gloss, tactile sensation, and marring resistance for polypropylene by incorporating a fatty acid amide-type lubricant such as erucamide (refer, for example, to Patent Document 10).
However, the use of an organic flame retardant, for example, a halogen-type flame retardant, with such blend formulations according to the prior art is still unsatisfactory in terms of performance: for example, a significant brown discoloration may be produced by the co-use of a fatty acid amide-type lubricant such as erucamide with a halogen-type (brominated) flame retardant. As a consequence, there is strong desire for a thermoplastic resin composition, for example, a polypropylene-based resin composition, that is free of discoloration defects, that is resistant to the staining and deterioration caused by urine, fecal matter, detergents, and so forth, that exhibits an excellent tactile sensation, and that is provided with marring resistance.